Stoker furnace



Jan. 13, 1931. w. c. DRAKE ETAL 1,789,223

STOKER FURNACE Filed sept. 26,' 1921 4 sheets-sheet 1 RGW: fA

Jan. 13, 1931. w. c. DRAKE ET Al..

STOKER FURNACE 26, 1921 4 Sheets-Sheet 2 Filed Sept.

.C DDAM/M6 BTP/magy) @13 INT0/omega) Jan' w. c. DRAKE ET AL 1921 4 sheets-sheet 4 Filed Sept 26 Q mi WW *CWM/A Patented Jan. i3, i931 unirse staresv maarre earanr carica WARREN o. nanna AND nnnnsrn. rnrnnn, or Inwoon, naw vom, lassenons 'ro FURNACE ENGINEERING COMPANY, INC.,

NEW YORK STOKER FURNACE Application filed September 28, 1921. Serial No. 503,334.

lThis inventionris an improved fuel burn'- ing furnace and relates to furnaces of various types, more especially to the modern coal burning, forced draft, progressive feed furnace, such for example as a boiler furnace supplied with fuel by an automatic stoking mechanism of the retort type, although the several features of inventionherein can in many cases be employed in other 'types and kinds o f furnaces.

The main object of the present invention is the general improvement in eliiciency, ease of operation and durability in furnaces. A particular object is the minimizing of a certain prevalent difficulty, namely, the-deposition of ferrous oxide, and formation of slag therefrom, on various parts of the furnace or boiler including the tubes of a tubular boiler. Another object is to secure the better distribution through the fuel bed of the fluid of combustion, air or steam, by ari-improved twyer system and control. Another object is to enable the direct introduction of steam into the body of the fuel bed for the improve; ment, in various respects, of the operation of the furnace; or a. combination of steam and air. Another object is to afford differential control in the admission of fluid of combustion, air or steam or both, at various particular parts of the fuel bed. Another obgect is to .minimize or prevent the formation of clinkers at the Walls of the furnace. Other objects and advantages of the present invention will appear 'in the hereinafter follow` ing description of one or more embodiments thereof or Will be apparent to those skllled in the art.

To the attainment of the above mentioned objects and advantages the present invention consists in the various novel features of, apparatus, mechanism, combination, arrangement or detail herein described or illustrated.

AFig. l is an interior side elevation of a furnace and stoker mechanism embodying the present invention, taken partly 1 n section on the plane l-l of Fig. 2; the innen-r tion being shown applied to a furnace having a Stoker of the retort type, with stationary retorts, and pushers working on the retort bottoms, such` for example as the well known show parts beyond.

Fig. 4 is an enlarged sectional View of one of the twyer constructions, shown in the same view as in Fig. 2a.

0F YORK, N. Y., A CORPORATIN 0F Fig. 5 is a bottom view of certain parts in Fig. fl.

Certain features xof the presentdmprovement may be embodied in other types of furnace and Stoker, for example in a furnace having the well known Riley type of Stoker in which the retorts have stationary bottom walls, but side walls which are reciprocated bodily with the twyer boxes.

Fig. 6 is a view similar to Fig. l but showin features of Ythe present invention embodied in the Riley type of stoker.

Fig. 7 is a transverse section taken on the plane 7-,7 of Fig. 6. l

Fig. 8 is a horizontal section on the'plane 8-8 of Fig. 'l'.

As will be seen, certain of thefeatures of the present invention, especially lpertainin to features of method and to the structure o the furnace side walls, or the twyers adjacent thereto, may be used on other types of progressive-feed furnace, for example a furnace with a traveling or chain grate, or a combination of underfeed stoker with chain grate.

Describing first the details of structure of the illustrated embodiments of this invention,

' twyer openings.

several throatsand rams, the rams all being operated by a common crank shaft 18. For each ram there is a crank or pin 19 connected by a pitman 20 with the ram. At a point further down and inward is shown a secondary ram 21 operated by a connecting rod 22 which is moved backwardly and forwardly froma lever 23 fulcrumed at 24 and oscillated by the connecting rod 20. The fulcrum 24v is at the forward end of a bar 25 to give a floating action. From-the lower end of the lever 23 extends a connecting rod 26, which in turn reciprocates a slide rod 27, which actuates a rock lever 28 in ausual manner, to reciprocate a socalled extension grate 29 located at the rear of the main grate and retorts, and between them and the usual dumping grate 30.

In all the figures the outline of thev fu'el bed is indicated by the broken line 31, thisl in some cases indicating two positions where the bed materially varies during operations.

The fuel forced into the furnace by the ram passes first over the bottom plate 32 of the throat, an'd thence over the secondary ram 21, and thence over the bottom plate 33 of the retort, and thence out of the retort upon- .which extends entirely across the Width of4 the furnace. Beneath the wind box is a large air duct 37 from which the various parts of the Stoker obtain their air supply. Thus from the main air duct 37 is shown a large upward pipe 38 leading to the wind box and containing a damper 39 which may be turned to different positions to control the air flow.

The damper has an operating arm 40 outside the pipe, and as shown in Fig. 1 a handle rod 41 at the front is accessible for regulating the same.

Four species of twyer construction are shown. The twyers and 75 adjacent to the side walls are of greater height than the others and Iserve additional functions, taking part in the effective prevention of clinker formation and attachment at the side Walls. These would be useful in any progressivefeed type of furnace, and other types. The intermediate twyers 45 and 45*1 are useful especially for the retort type of underfeed furnace, but the principles could be adapted to other uses.

Referring first to the twyer 45, this is shown as comprising a generally .lit-shaped structure, being built up of a number of castings of this shape, set upright and placed in face Contact, as indicated in Fig. 3. Air apertures into the fuel bed are provided along the height of each twyer member. For rea'- sons that will appear these apertures may be grouped into upper apertures 46 and lower apertures 47.v They may be formed by means of registering grooves at the contacting ver-v I the direction of fuel travel, and the apertures may be tapered and graduated in size. These remarks apply not only to the twyer 45 here-`\ ofbutalso the other forms of twyer.

An important feature of this invention is a novel air distribution and regulation, with differential pressures, as will be described. This is controllable, preferably at will, according to conditions in the furnace. Air is introduced into the fuel bed from the twyers at different heights or depths. My method is normally to providegreater pressure at the greater depth of fuel so as togive more complete air distribution and more perfect.

combustion. In some instances, however, an excess depth of fuel may form, perceived by the attendant, and my invention enables this to be eliminated by causing the burning down of the excess fuel b reversing the differential pressures, intro ucing air at greater pressure at the upper part gf the twyers.

For the purpose ofv carrying out this method and structure each twyer is shown as havino' its` interior space divided into upper and lower chambers or divisions, separately controllable. Thus the twyer 45 is shown as having a division plate 48 extending interiorly across its width and lon 'itudinally throughout its length. This dlvision plate or partition is shown in the form of a channel with its side anges extending upwardly. Each of the opposite inclined sides of the twyer member has interior fingers 49 extending downwardly to hook over the channel 48 and give additional support to the twyer. The channel or division plate 48 is of course inclined rearwardly, as are 'the retort and twyer box, and its lower and upper ends may be secured by bolts 50 and 5l. This division wall 48 separates off the upper part of the twyer box 35, forming an upper chamber 53. lt will be noticed that the upper series of apertures 46 emerge from 'the upper chamber while the lower series 47 e lugs 56.

mamas give exit of air from the lower or main chamber 35.

To admit air to the upper chamber the division plate 48 is provided with a series 0f passages 52, and to regulate the flow a sliding damper 54 is provided at the under side of the plate. ln this way the flow of air to the upper twyer apertures 46 may be relatively decreased so' that the lower apertures will receive the greater pressure. This conduces to the eiciency of the furnace since the. lower apertures, being at the greatest depth of f uel, require the greater pressure to forcev the air into the fuel. Therefore, a much more thorough and uniform distribution is secured. Air at a lower pressure will pass from the Lipper apertures intothe fuel with comparative readiness. This differentiation of pressure according to position or depth of the apertures is animportant featureof the present invention; also the damper control giviug relative regulation is important, owing to 'the constantly changing conditions within the furnace.

The damper 54 is shown as consisting of a series of short damper members connected together by a rod 55. The rod has vlugs .i6 formed on it, affording stops to limit its movements in opposite directions. rIhe underside of the division plate 48 has also a series of lugs 57. These extend downwardly and are perforated to receive the rod 55. The rod thereby slidesl through the lugs 57 and these lugs cooperate with the' stop At its upper or forward end the damper 54 is shown provided with an operating rack 58, as seenl in Fig; 3, engaged by a toothed segment 59 pivoted at 60 and operated by a handle rod 61 accessible from the exterior to shift the damper 'and thus control thc relative air pressure and fiow in the upper and lower chambers respectively of the twyer box.

This described differential regulation of i pressure according to depth involves -a greater pressure at the greater' depth, but later. will be described how a greater pressureat a greater height will be obtained at a given part of the furnace for breaking down a temporary excessive depth of fuel.

The second ofthe intermediate twyers as seen in Fig. 2b is substantially the same as the twyers excepting that the two sloping side portions are shown as separate castings 45Ei and 45", with an interlocking cap plate 45e, or rather a series of them, as shown 1n the middle part of Fig. 3, and generally like those shown in said prior Patent :No 1,360,250.

At the two side walls are shown special twyer constructions, with air directed inwardly and upwardly into the fuel bed, and interior division into upper and lower chambers. These constructions not only give the advantages already mentioned, but give substantial improvement in minimizing clinker formation at the side walls. The admission of air or steam at the side walls not merely improves combustion so as to minimize elinkers,but gives ample air iow along the side walls, protecting them from the tendency to fuse and unite with clinkers. For such purposes the construction herein shown is de-` cidedly superior tothat shown in the prior patent.

Two forms of side wall twy-ers are shown in Fig. 2. and that at the 'right is also seen in Fig. 1. Each of the side wall twyers is shown as of considerably greater height than the intermediate twyers. They may be formed of castiron, as are the others, and may be set directly alongside the refractory wall 13 or in somev cases may be partly or wholly inset or built into the wall. The cast iron is amply protected bv the flow of air,

and as stated the result of the'action is the protection of the refractory walls'at points above the twyer upward to the top level of the fuel bed.

The side wall twyer 65 at the left is shown as having upper groups ofapertures 66 and lower groups 67 directed effectively into the fuel` bed. With its inclined shape and integral top portion the twyer 65 may be described as similar to one half of the twyer vthe parts.

The division wall 69 divides the interior space of twyerl 65'into an-upper-chamber 73 and a lower chamber 74, which latter includes the space above-the open flange or wall 70. Associated with the partition wall 69 is a damper 54 for regulating the pressure and relative flow of air in the upper and lower chambers. This for convenience is shown as the same in structure and operation as the Si)l damper 54 already described inconnection vwith the twyer 45 The side wall tv s yer 75 shown at the right side of Eig. 2b is in some respects similar to the twyer 65 at the left.V Tt shows the similar series of upper apertures 76 andl lower apertures 77. The twyer member also rests uponA an L-shaped casting 78. This casting has a horizontal fiange 79 which may serve as a partition wall, and a lower flange 80 of open construction, engaged by fingers 8l ,formed on the twyer member. y this construction the interior space is divided into an. upper which otherwise are carried with the furnace chamber 83 and a lower chamber 84. In this embodiment is shown a separate means of conducting air from a point below the lower chamber to the upper chamber, and therefore it would be unnecessary to provide openings and a damper 54 at-the division wall 7 9, but as in some cases this may be of additional advantage we have shown such a damper 54, together with the elements 55 to 61 tor operating it, similar to the connection for operating the dampers 54.

There will now be described the preferred means of producing an excess of air pressure and flow at the upper part of the twyers. This additional air of combustion' introduced at the proper point will tend to burn down any excess depth of fuel, as explained.

This condition is met-herein by closing the twyer division wall and providing air of greater pressure in the upper twyer chamber than at the lower chamber.

vThus for the twyer 75 at the right of F ig. 2b is shown an air passage 85, of ample dimension, leading from lthe main air duct 37 directly through the furnace side wall and `into the upper twyer chamber83. As this, however, may be of only temporary service We have shown adamper 86 in the passage 85. The passage above the damper is indicated by the numeral`87. Ordinarily itmay be sufficient to pass air from the wind box 36 through a short passagel 88 directly into the passage 87 and thereby to the upper twyer chamber. A damper 89 is shown in A the passage 88 for cutting olf this passage when the air at greater pressure is introduced directly from the air duct 37 A similar provision of high pressure air to the various other twyer members may be made, so that the entire area of the Jf'uel 'bed is thus controllable. The pipes 93 and 97 hereafter mentioned may be used for this purpose.

Another part of this invention is the direct introduction of steam into thebed of burning fuel. lA proper quantity of steam so introduced assists the combustion, but moreover tends to decompose certain products gases and deposit themselves on walls, boiler tubes, etc. The introduction of the steam eliminates the deposits or renders them friable and easily or automatically removable. Ferrous oxide is believed to be one of the worst sources of trouble, especially in its forming of a slag upon the boiler tubes, to the great detriment of efficiency; and this invention breaks down this substance by the decomposing action of the steam introduced into the burning fuel. y According tofthis invention the steam in vaporous condition is introduced into the 4 twyer? boxes, preferably by steam conduits leading directly into the interiors of the u per twyer chambers 53, 7 3 and 83, from whic 53. Each pipe may have a number of dis` tributing apertures to pass the steam into the chamber along its length. Each steam pipe may be bent downwardly at its upper end as indicated in Fig. 3, so that this element may be utilized as the upper holding bolt 51. The extremity of this pipe may be -connected by a header 94 with a main steam feed pipe 95.l The' steam and air supply therefore are independent, buteach ofcourse is fully regulable by means of the usual steam valves and air dampers.

In the side wall twyer box 73 is shown a similar steampipe 97. The steam admitted pose mentioned but also to promote combustion adjacent to the side wall, thus. tending to minimize clinker difficulties.

With the bther illustrated side wall twyer 83 the steam pipe 99 is shown as supplied by horizontal pipe 100 'and a vertical extension 101 controlled by a valve 102, these sup-v plied rom the main steam feed pipe 95.

A moderate quantity and pressure of steam will serve the purposes hereof, and practice will determine the best regulation or any given conditions.l y

-In Figs. 6, 7 and 8 are shown features of the present invention applied to the Riley type of stoker. The underfeed mechanism may be similar to the other figures. The retort bottom plate 33, however, is stationary in the Riley Stoker while the retort side walls 34:

The side wall twyer 65 is similar to that-at the left of Fig. 2 having the upper and lower series of apertures and the u per chamber 53 formed by the division wal 69 and the lower chamber 74' connected with the wind box. Al'so `associated with the partitionwall is the sliding damper 54 operable by the exterior handle rod 61 to control the relative air pressures withinthe upper and lower chambers. y

For use in connection with any of the described side lwalltwyers, or inA some cases in lieu of them, we have provided air supplying structures or twyer boxes embodiedA or linset directly in. the side walls. For examin shown as formed of cast iron. It serves tov admit air or steam or a combination of air and steam directly into the fuel at the side wall for promoting combustion and minimizing clinler difficulties, and as stated it may be used in conjunction with a twyer `located within the furnace directly adjacent to the sidewall, as shownin Figs. 6 and 7. It is believed to be new to use in combination a twyer construction alongside a wall and another within or forming part of the wall.

This part of the invention may be embodied in the side wall by means of an elongated inclined cast iron air box 105 which in cross section is shown as somewhat of the shape of the letter E. The upper flange 106v is of stepped formation, having alternate short horizontal and vertical portions as seen in F ig. 6, so as conveniently to combine with l -the refractory bricks or tiles of which the wall (lll it is shielded from the fuel bed by'a series of protecting tiles or refractory bricks 107. -The bottom flange 10S of the wall box may be of stepped form similarly to the top flange and at one or more points it has a large aperture 109 to receive air under pressure through a. wall passage 110 controlled by damper 111 regulated by an exterior handle 112.

The middle fiange 113 is not stepped but extends first horizontally and then downwardly at a slant and it has a series of openings 114 so as to admit air from the lower chamber to the upper chamber of thevbox. The inner extremity of the flange 113 is enlarged at 115 for the purpose of positioning and locking the upright twyer. bars 117. These bars are stacked in face Contact, and

yform the effective air supplying face of the furnace wall. Each of them is provided with an upper series. of side grooves 1 18 and a lower series 119 affording tapered passages from 'the upper and lower chambers respectively, directly into the fuel bed. Also each bar may' have a small groove 120 at its top. Each bar has a 'pair of interior fingers or hooks 121 engaging the enlargementfll for the purpose of positioning and holding the twyer bars in position. The barsmay be strung onto the middle'flange 113 at its upper end and slid into position.

The side wall box 105 is of such shape as substantiall to correspond with the fuel bed line 31 so t iat the air or steam or both are effectively introduced into the fuel. at all points along the side walls from the front to the rear of the furnace.

In order to regulate the relative air pressure in the upper and lower chambers, a damper 123 is shown beneath the perforated Harige 113, and this may be regulated by a I handle 124.

4 It is practically of value, especially for the reasons already mentioned to introduce steam into the fuel bed and for this purpose a longitudinal steam pipe 126 is shown within the side wall box, the same supplied by a pipe 127 leading through the wall and a vertical pipe 128 controlled by a valve.129.

It will thus be seen that a fuel burning apparatus has been described embodyin the principles and attaining the objects o the present invention. Since many matters of construction, combination, arrangement, operation and detail may be modied without departing from the principles involved it is not intended to limit the invention to such features except so far' as pended claims. What is claimed is:

apartvtwyer structures 'supporting the fuel bed, twyer apertures at different altitudes in a twyer struct-ure, and means to cause a difference in pressure of air supplied to the apertures of greater and lesser altitude respecf tively. i

2. In a forced draft furnace having spaced apart twyer structures supporting the fuel bed, the samehaving upper and lower apertures, and means to supply .air to. said apertures with the greater air pressure to the lower apertures.

3. A furnace as in claim'l' and wherein means are provided to relatively regulate the pressures during combustion.

4. In a multiple retort furnace having means for underfeeding coal into the retorts,

' and means for maintaining` travel of the fuel bed, a. series of twyer boxes forming retorts between them, each, twyer box being divided into separate chambers, air supply means for Aone chamber in each twyer box and separate connections for supplying steam to another chamber in each twyer box, for injection into the fuel bed at .distributed -noint's throughout its width.

5. In a furnace the ,combination furnace wall,"a twyen structure extending between the fuel bedv and Wall and admitting air to the fuel bed and an air injecting structure in the wall above the level of said twyer structure, with apertures leading directly into the fuel bed.

6. In a retort furnace a series of twyer boxes forming retorts between them, a division Wall within a'twyer box dividing it' into upper and lower chambers, means to .supply forced draft to the lower chamber,

anda draft regulator between the chambers.

7. In a` retort Ifurnace a series of twyer boxes forming retorts between them, a division wall within a twyer box dividing it into upper and lower chambers, means to supply forced draft to the lower chamber,

specified in the apof the l5 v 1. In a forced draft furnace having spaced 'e' supplying air to the.structures, a partitiony separating al structure into upper and lower chambers, with twyer apertures both above and below the partition, at different depths beneath the fuel bed and an air passage to 10 1the upper chamber.

9. Furnace as in claim 8 and wherein are means for regulating at will the relative pressures of air to the upper and lower chambers.

10. In a retort furnace a series of'twyer boxes forming retorts between them, a division wall within a twyer box dividing it into upper and lower chambers, means to sup'ply forced draft to the lower chamber, and a separate means to supply steam to the upper chamber.

11. In a furnace having twyer boxes forming retorts between them, an arrangement with the' extreme boxes closely adjacent the side walls and substantially higher than the intermediate boxes but not as high as the .fuel bed top level, such side wall boxes having division walls separating their interiors into u per and lower chambers.

12. n a furnace having twyer boxesforming retorts between them, an arrangement with the extreme boxes closely adjacent the side walls and substantially higher than the intermediate boxes but not as high as the fuel bed top level, such side wall boxes having division walls separating their interiors into upper and lower chambers 'and connections for supplying Huid at different pressures into the two chambers.

13. In a furnace having twyer boxes forming retorts between them, an arrangement with the extreme boxes closely adjacent the side walls and substantially higher than the intermediate boxes but not as high as the fuel bed top level, such side wall boxes having division walls separating their interiors into upper and lower chambers, and separate Huid connections to the two chambers.

14. In a furnace having twyer boxes forming retorts between them, an arrangement with the extreme boxes closely adjacent the side walls and substantially higher than the intermediate boxes but not as high as the fuel bed top level, such side wall boxes having division walls separating their interiors into upper and lower chambers, an air connection to the lower chamber, and a steam connection to the upper chamber.

15. In a forced draft furnace, the furnace side walls, and the grate between them, having parallel retorts, separated by twyer structures, and comprising a twyer structure extending upwardly and outwardly substantially to the wall, substantially higher than the other twyers, and a hollow metallic box in .thek side wall immediately above such twyer structure with apertures directed into the fuel bed, and means conducting fluid under pressure thereto, said side wall box having a fuel contacting face composed of .a series of separate, narrow, upstanding xder pressure thereto; the twyer structure being an iron structure extending at a slant upwardly to a point substantially higher than the normal height of the grate and perforated to admit air to the fuel supported by it,

'and the hollowwall structure being an iron bOx set in the side wall between thetwyer structure and the fuel bed top level.

17. In a forced draft furnace, the furnace side walls, and the grate between them, comprising a twyer structure extending upwardly and outwardly substantially to the wall, and a hollow structure in the side wall above such twyer structure with apertures directed kinto thefuel bed, and means conducting fluid under pressure thereto; the hollow side wall structure being built up of numerous upstanding bars assembled in face contact and secured together.

18. In a forced draft retort furnace, the furnaceside walls, and the retort grate between them, the grate comprising a perforated twyer structure extending upwardly and outwardly from a retort substantially to a side wall, and said side wall embodying a hollow wall portion immediately above such twyer structure, the same composed of an assembled series of wall members and formed withnumerous perfor-ations for delivering fluid jets directed into the fuel bed, and means conducting fluid under pressure thereto and to such twyer structure.

19. Iii a Stoker` furnace, the furnace side walls, and the grate between them inclined toward-the discharge, comprising a reciprocable twyer structure extending upwardly and outwardly to the side wall, and entering y twyer structure, the same extending slantingly from the adjacent retort upward to the side wall but terminating substantially below the top of the cool bed, and the side wall, the same formed with a wall section extending between the top of the extremetwyer structure and the top .of the coal bed having air oirculation passages to constitute it an air cooled wall section, for the prevention of clinkers on said wall, and means supplying air to said twyer structure and to said air cooled wall section.

21. In a forced draft furnace, the furnace side walls, and the grate between them, comprising a twyer structure extending upwardly and outwardly substantially to the wall, and a hollow structure in the side wall above such twyer structure with apertures directed into the fuel bed, and means conducting fluid under pressure thereto; the hollow side wall structure being built up of numerous upstanding bars assembled in face contact and secured together, said bars having face grooves forming the apertures into the fuel bed.

22. In a forced draft furnace, the furnace side walls, and the grate between them, comprising a twyer structure extending upwardly and outwardly substantially to the wall, and a hollow structure in side wall above such twyer structure withV apertures directed into the fuel bed, means dividing the hollow structure into compartments, means conducting fluid under pressure to said hollow structure, and means affording different pressures in such compartments thereof.

23. In a forced draft furnace, the furnace side walls, and the grate between them, comprising a twyer structure extending upwardly and outwardly substantially to the wall, and a hollow structure in the side wall above such twyer structure with apertures directed into the fuel bed, means dividing the hollow structure into compartments and means conducting air to one compartment and steam to another.

24. In a multiple retort progressive feed furnace having means for underfeeding coal into the retorts, a plurality of spaced apart twyer structures between the retorts and v supporting the fuel bed, said twyer structures each having interior air passages and a set of air a ertures therefrom delivering air into the a vancing fuel bed and having separate interior steam passages and a set of steam apertures therefrom for delivering steam into the advancing fuel bed, and separate regulable connections for supplying air and steam respectively to said passages to be delivered directly into the advancing fuel through such respective sets of twyer apertures at distributed points throughout the width of the fuel bed.

Q5. In a multiple retort furnace a system of twyer structures with fuel retorts between them, and air boxes beneath the twyer strucover such upper-outer portion thereof, and

enclosing an air space, a wall dividing such air space into upper and lower compartments, and damper means in such dividing wall for varying the air pressure in the up'- per compartment of such air space.

26. A progressive feed Stoker furnace having in combination with its enclosing walls,

a system of air boxes and twyer members' forming retorts inclined downwardly from the front toward the rear, means for feeding coal at the front into the retorts and for maintaining progressive travel of the coal bed toward the rear, an air box between each extreme retort and the adjacent side wall and a twyer structure extending' upwardly from such retort to such wall, the same slanted downwardly toward the furnace rear, all said twyer members and air boxes being located a. substantial distance below the coal bed line; and each side wall embodying a hollow fluid-cooled clinker-preventing metallic wall structure built up of a system of wall members assembled in mutual contact, and said structure extending substantially from the top f the side wall twyer to the top of the coal bed and stepped downwardly to the rear with a trend substantially parallel t0 the slant of the retorts, and the stepped upper side of such structure having substantially horizontal supporting surfaces giving support to the side wall elements or bricks thereabove; and means for supplying cooling fluid for circulation through such hollow structure. j

In testimony whereof, we have afiixed our signatures hereto.

IVARREJ C. lDRAKE, ERNEST B. PRIEBE. 

